Mechanical coupling for cooperating rotatable members

ABSTRACT

A mechanical coupling to transfer torque between cooperating rotatable members each of substantially circular cross section and aligned along an axis of rotation comprises first and second members including, respectively, first and second surface portions in juxtaposition across an interface. Each surface portion includes a plurality of spaced apart teeth mechanically interlocking at the interface. The first surface portion comprises a fiber reinforced material including fibers oriented within about 45°, on either side, of an axis of rotation. Provided is a clamp to hold the first and second surface portions together at the interface.

The Government has rights in this invention pursuant to Contract No.F33615-94-2-4439 awarded by the Department of the Air Force.

BACKGROUND OF THE INVENTION

This invention relates to a coupling between a plurality of rotatablemembers of generally circular cross section. More particularly in oneform, it relates to a coupling between aligned, co-operating members ofa shaft.

In rotating apparatus, for example shafts, drums, etc. in powergeneration machinery such as a turbine engine, it can be desirable tojoin cooperating, rotating members of dissimilar materials, metals oralloys. Examples of such rotating members include shafts, drums, conicalstructures, etc., designed in various forms within a gas turbine engine.A variety of reported methods for bonding such dissimilar metals andalloys include diffusion bonding, conventional welding, frictionwelding, brazing, and explosive bonding, depending on such conditions asthe intended operating temperature of a component being formed and themechanical properties required in the joint between such members. Whensignificant differences exist in properties, such as in strength,thermal expansion, etc., transition metals or metal alloys have beenbonded between members.

In modern gas turbine engines, it can be beneficial, for example forweight reduction, to use for a rotating component, such as a shaft, acombination of a metal or metal alloy member and a fiber-reinforcedmember, such as a metal matrix composite, carried together for rotation.One example of such a composite known in the art includes a matrix basedon Ti or an alloy of Ti, reinforced with fibers, for example glass,graphite, carbon, polymer, metal, etc. Bonding, such as the typesidentified above, does not provide adequate mechanical and/or physicalproperties to a joint between such members of significant differences inthermal expansion characteristics. Such bonding particularly is aproblem when it is intended to transfer torque between such cooperating,dissimilar members during rotation.

BRIEF SUMMARY OF THE INVENTION

The present invention, in one embodiment, provides a mechanical couplingto transfer torque between cooperating rotatable members, each ofsubstantially circular cross section and aligned along an axis ofrotation. The coupling as a combination comprises a first member havinga first surface portion of a fiber reinforced composite materialincluding fibers oriented predominantly within about 45°, on eitherside, of the axis of rotation. The first surface portion includes afirst plurality of spaced-apart teeth projecting from the first surfaceportion, in one form generally axially and disposed generallycircumferentially about the first member.

The coupling comprises a second member having a second surface portionincluding a second plurality of spaced-apart teeth projecting from thesecond surface portion toward the first plurality of teeth, in one formgenerally axially and disposed generally circumferentially about thesecond member. The first and second plurality of teeth cooperate injuxtaposition to interlock one with the other defining an interfacebetween the first and second members. Clamping means holds the first andsecond members together at the interface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic, fragmentary view of a hollow shaftsubstantially of circular cross section comprising first and secondshaft members joined at a radial spline therebetween, according to aform of the present invention.

FIG. 2 is a diagrammatic fragmentary view of the shaft of FIG. 1 showinga form of holding means or fastener holding members of the shafttogether.

FIG. 3 is a fragmentary, sectional view of another form of holdingmeans.

FIG. 4 is a graphical presentation of data comparing torsional strengthand modulus with fiber angle of orientation relative to the axialdirection or axis of rotation for a Ti metal matrix composite shaftmember.

FIG. 5 is an enlarged, fragmentary sectional view of a portion of theradial spline of the type shown in FIG. 1.

FIG. 6 is a fragmentary, sectional view of another form of themechanical coupling of present invention.

DETAILED DESCRIPTION OF THE INVENTION

An advantage of replacing at least a portion of a member of a gasturbine engine, intended for aircraft application, with a relativelylower mass composite material is reduction in weight. Other advantagescan include higher shaft stiffness and reduced cost. One example of sucha member is a rotating shaft intended to transfer torque from one engineportion to another, such as between a front fan and a low pressureturbine of a gas turbine engine. Permanent bonding, such as by welding,of a fiber reinforced metal matrix composite portion of a rotating shaftto a metal or metal alloy shaft portion of generally uniform structureis not practical, and in some examples cannot be accomplished, forcertain shafts of a gas turbine engine. The present invention provides amechanical coupling that enables the transfer of torque between suchcooperating rotating members. In addition, the mechanical arrangement ofthe invention provides the capability to compensate, in the couplingdesign, for tolerances associated with differences in thermal expansioncharacteristics between the cooperating members.

The present invention will be more fully understood by reference to thedrawings. FIG. 1 is a simplified, diagrammatic fragmentary view of ahollow, rotating shaft of substantially circular cross section, showngenerally at 10. Shaft 10 comprises a first hollow member 12 with anouter wall 14 and made of silicon carbide fiber reinforced matrix of acommercial Ti base alloy. Other fibers that can be used includegraphite, carbon, tungsten, polymer, boron, and glass. Shaft 10 includesa second hollow member 16 with an outer wall 18 and made of a Ni basealloy commercially available as In 718 alloy. Typical examples of metalsfrom which second member 16 can be made include at least one of Fe, Ni,Co, Ti, Al, Mg, and their alloys. Fibers in the matrix of member 12,when oriented generally axially not only provided a member as 12 ofabout 60% of the weight of the Ni alloy member 16, but also up to abouttwice the stiffness of member 16.

To provide the mechanical coupling of the present invention, the firstand second members 12 and 16, respectively, are disposed interlockingthough releasable registry, as shown, in the form of a mechanical radialspline, representing the coupling, shown generally at 20. Spline 20comprises a first plurality of teeth-like members 22, herein calledteeth, circumferentially disposed about first member 12 and projectingfrom first member 12 generally axially in respect to shaft axis ofrotation 24. Spline 20 also includes a second plurality of teeth 26,mechanically to interlocking with first plurality of teeth 22,circumferentially disposed about second member 16 and projecting towardteeth 22 generally axially in respect to shaft axis of rotation 24.Teeth 22 and 26 interlock at radial spline 20 to define an interface 27between members 12 and 16. Holding the first and second members forrotation together and transfer of torque is a clamping means representedin FIG. 1 as arrows is 28. Forms of such clamping means are shown inFIGS. 2 and 3.

The embodiments of the drawings are presented as hollow shafts becausethat form is most frequently used in aircraft gas turbines. However, itshould be understood that the present invention can be applied tosubstantially solid type shaft members as well. Examples of hollowshafts have been designed to operate and rotate within a gas turbineengine between the fan section and turbine section of the engine, as iswell known in the turbine engine art. As mentioned above, in priordesigns such a hollow shaft has been made of a single metal or alloy, ora plurality of cooperating metal and/or alloy members aligned and bondedinto a shaft, such as by welding or other fusion bonding.

The fragmentary, diagrammatic view of FIG. 2 shows the combination ofmembers of FIG. 1 in which the clamping means 28 included in themechanical coupling of the present invention is a cap screw fastenerincluding collar 30 about interlocked teeth 22 and 26 of spline 20.Collar 30 is secured about shaft 10 at spline 20 by a screw 32.

Another embodiment of clamping means 28 is shown in the fragmentarysectional view of FIG. 3. In that form, walls 14 and 18 are clampedtogether across interlocking interface 27 by threaded screw 34.

According to embodiments of the present invention, reinforcing fibers infiber reinforced composite first member 12 are aligned generally alongaxis of rotation 24 predominantly within about 45°, on either side, ofthe direction of the axis of rotation. The presentation of FIG. 4includes data from a graphical comparison of torsional strength andmodulus with fiber angle relative to axial for a fiber reinforcedcomposite. The matrix of the composite was a commercial Ti base alloy,for example Ti 6-4 alloy and Ti 6-2-4-2 alloy. The reinforcing fiberswere silicon carbide. The data of FIG. 4 show that the torsionalstrength and modulus preferred for the coupling of the present inventionis attained when the fibers are aligned within about 45°, on eitherside, of axial. According to a form of the present invention, fiberangle was selected to satisfy torque and stiffness requirements. Fiberspredominantly in the longitudinal direction provided the higheststiffness. The highest torque capability was achieved with fibers atabout 45° to the axis of rotation.

FIG. 5 is an enlarged fragmentary sectional view of a portion of theinterlocked members of FIG. 1. Teeth 22 and 26 are releasablyinterlocked mechanically at interface 27 between members 12 and 16,respectively. Shown in FIG. 5 are reinforcing fibers 26, alignedgenerally along axis of rotation 24. Arrows 38 and 40 show the directionof torque respectively for members 12 and 16.

FIG. 6 is a fragmentary sectional view of a wall of another embodimentof the present invention in which a fiber reinforced first member 12 ismechanically coupled at teeth 22, as described above. In this example,first member 12 is interlocked between cooperating second member 16 anda third member 42 including teeth 44. Each of members 16 and 42 is madeof a metal or metal alloy generally of uniform structure. The mechanicalcoupling is held by clamping means 28, for example as described above.

The present invention has been described in connection with specificexamples and embodiments that are intended to be typical of rather thanin any way limiting on its scope. For example, forms of the mechanicalcoupling of the present invention can be used at any joint in which itis intended to transform torque into a cylindrical form. Those skilledin the art will understand that the invention is capable of variationsand modifications without departing from the scope of the appendedclaims.

What is claimed is:
 1. A mechanical coupling to transfer torque betweencooperating rotatable members, each of substantially circular crosssection and aligned along an axis of rotation, the coupling comprising:a first member having a first surface portion of a fiber reinforcedcomposite material including fibers oriented predominantly within about45°, on either side, of the axis of rotation; the first surface portionincluding a first plurality of spaced apart teeth projecting from thefirst surface portion; a second member having a second surface portionincluding a second plurality of spaced apart teeth projecting from thesecond surface portion toward the first plurality of teeth; the firstand second plurality of teeth cooperating in juxtaposition to interlockmechanically one with the other defining an interface between the firstand second members; and, clamping means to hold the first and secondmembers together at the interface.
 2. The mechanical coupling of claim 1in which: the first plurality of teeth project generally axially and aredisposed generally circumferentially about the first member; and, thesecond plurality of teeth project generally axially and are disposedgenerally circumferentially about the second member.
 3. The mechanicalcoupling of claim 1 in which the first surface portion of the firstmember is a fiber reinforced metal matrix composite material comprisingthe fibers in a metal matrix.
 4. The mechanical coupling of claim 3 inwhich: the metal matrix is based on Ti; and the fibers are at least oneselected from the group consisting of silicon carbide, graphite, carbon,tungsten, polymer, boron and glass.
 5. The mechanical coupling of claim4 in the form of a turbine engine shaft in which the second portion ofthe second member is made of at least one metal selected from the groupconsisting of Fe, Ni, Co, Ti, Al, Mg, and their alloys.
 6. A rotatablegas turbine engine shaft of substantially circular cross sectioncomprising the mechanical coupling of claim 1, including the firstmember and the second member of the mechanical coupling, the firstmember and the second member each being of substantially circular crosssection, the first and second members secured to rotate in registrytogether through the mechanical coupling.
 7. The shaft of claim 6 inwhich: the first member is hollow and is a fiber reinforced metal matrixcomposite material comprising fibers in a metal matrix, in which themetal matrix is based on Ti and the fibers are at least one selectedfrom the group consisting of silicon carbide, graphite, carbon,tungsten, polymer, boron, and glass; and, the second member is hollowand is made of at least one metal selected from the group consisting ofFe, Ni, Co, Ti, Al, Mg and their alloys.
 8. In a method for making themechanical coupling of claim 1, including the first member and thesecond member of the mechanical coupling, the steps of: selecting thefiber reinforced composite material for the first member; selecting ametal for the second member; selecting torque and stiffness requirementsfor the coupling; measuring and comparing, for the fiber reinforcedcomposite material, the torsional strength and modulus with fiber angleto provide comparison data; and then, selecting from the comparison dataa fiber angle within about 45° of the axis of rotation for the fiber inthe composite material for the first member to satisfy the torque andstiffness requirements for the coupling.
 9. The method of claim 8 formaking a rotatable gas turbine engine shaft of substantially circularcross section comprising the first member and the second member eachbeing of substantially circular cross section, the first and secondmembers secured to rotate in registry together through the mechanicalcoupling, wherein: the fiber reinforced composite material of the firstmember comprises the fibers in a metal matrix based on Ti; the fibers ofthe fiber reinforced composite material of the first member are at leastone selected from the group consisting of silicon carbide, graphite,carbon, tungsten, polymer, and glass; and, the second member is made ofat least one metal selected from the group consisting of Fe, Ni, Co, Ti,Al, Mg and their alloys.